Research of obtaining pseudo-CT images based on ultrasound deformation fields in radiotherapy

Objective: An improved method for obtaining pseudo-computed tomography (CT_ps) based on ultrasound deformation field. Methods: The three-dimensional image data of computed tomography and ultrasound for three postoperative cervical cancer patients were selected, including the CT (CT_sim) and ultrasound (US_sim) images obtained during the simulated positioning stage, and the cone beam CT (CBCT) and ultrasound images obtained during the positioning verification stage of the treatment one week later. Binary masks of the OROI and OROW were created and applied in ultrasound image registration;thus, the deformation field was obtained. The deformation field was applied to CT_sim images and different pseudo-CT images were obtained. Similarities between these pseudo-CT images and those of CBCT were compared, and registration accuracies between pseudo-CT images under different binary masks and CT_sim were discussed. Results: The averages of the correlation coefficient between pseudo-CT based on OROI, OROW, no binary mask and CBCT were 0.95, 0.82 and 0.64 respectively. The average of the normalized mean square Error were 0.12, 0.42 and 0.57 respectively. Conclusion The pseudo-CT based on OROI binary mask matches the best with CT_sim and achieves the highest similarity with CBCT. (authors)